Mobile wireless communications devices typically employ diversity, a technique used to compensate for fading. In space diversity, multiple transmit antennas are employed, spaced so that the signals from each transmit antenna to receive antenna are likely to be uncorrelated with each other. In time diversity, information is repeatedly transmitted at time spacings that exceed the coherence time of the communications channel; consequently, multiple representations of the symbol are received under independent fading conditions, thus providing diversity. Space time transmit diversity (STTD) employs both space and time diversity.
Diversity schemes, such as STTD, may employ two or more equalizer filters running in parallel off the same filter delay line, each with a corresponding post-equalizer processor such a descrambler/despreader. Each equalizer filter and post-equalizer processor is typically implemented in a separate hardware block on an integrated circuit chip. Since the primary diversity mode, such as STTD, is not always used, the additional equalizer filter(s) and post-equalizer processor(s) represent a waste of space and power. Solutions have been proposed which partially address the power consumption issue, but these have disadvantages, and have not addressed the waste of space on the integrated circuit chip.
Accordingly, it would be desirable to provide a reconfigurable communications circuit where use can be made of the hardware blocks for the extra equalizer filter(s) when not in the primary diversity mode, making appropriate trade-offs between performance and power consumption.